Axle assembly cooler using parallel flow paths

ABSTRACT

A work vehicle includes a frame and an axle assembly coupled to the frame. The axle assembly includes a first axle shaft and a first axle housing, with the first axle shaft disposed substantially within the first axle housing; a first wheel coupled to the first axle assembly; an axle lubricating fluid disposed within the first axle housing; and a first axle cooling device disposed within the first axle housing, in contact with at least a portion of the lubricating fluid, and including a first coil. Also disclosed is a method of cooling an axle assembly of a work vehicle. The method includes steps of removing heat from the lubricating fluid by placing the lubricating fluid in contact with the outer surface of a coil, and removing the heat from the inner surface of the coil by circulating the cooling fluid through the passage.

This is a Division of application Ser. No. 09/525,818, filed Mar. 15,2000, now U.S. Pat. No. 6,499,565.

FIELD OF THE INVENTION

The present invention relates generally to the field of work vehicles.It relates more particularly to removal of braking heat from an axle ofa wheeled loader.

BACKGROUND OF THE INVENTION

Some work vehicles, such as end loaders, must change their directions ofmovement frequently. To do this, wheel or live axle brakes are generallyused to first bring the vehicle to a stop. When this is done frequently,the brakes become overheated.

This has sometimes been resolved by placing the brakes inside an axlehousing, where the heat generated by brake friction is removed from thebrake by an axle lubricating bath. The lubricant spreads the heat overthe entire interior surface of the axle housing, whereupon thermalconduction through the walls of the axle housing heat the exteriorsurface of the axle housing and provide increased surface area for heatto be convected away by ambient air.

In some instances, however, convection to and from the axle housingsurfaces is insufficient to remove braking heat rapidly enough, and theaxle lubricant consequently becomes excessively hot (e.g., above 300degrees Fahrenheit). This is injurious not only to the lubricant itself(accelerating oxidation and breakdown), but also to the bearings andseals associated with the axle shaft.

Typically, the brake is a wet multiple disk brake; “wet”, because thedisks rotate through a bath of lubricating oil. As the multiple brakedisks rotate through the lubricating oil, braking heat is transferredfrom the disks to the lubricating oil.

The temperature of the lubricating oil consequently increases, and someof the heat within the lubricating oil is transferred to the axle shaftand to the axle housing. The axle shaft and axle housing are of limitedsize and mass and, hence, of limited heat capacity. Therefore, theirtemperatures begin to approach (under the duty cycle of frequent stopscharacteristic of a loader) the temperature of the lubricating oilbecause ambient air typically does not convect heat from the axlehousing as rapidly as the brake convects heat into the lubricating oil.It is therefore necessary to actively cool the lubricating oil.

While one can add a cooling loop to an axle assembly and pump hotlubricating oil through a fan-cooled radiator, this is a costly andcumbersome approach. Further, it increases the number of opportunitiesfor leakage or contamination of the lubricating oil in what is typicallya dirty and dusty environment.

It would be advantageous to provide an apparatus and method of removingexcessive heat from the axle lubricant, thereby cooling the axleassembly, without substantially increasing the risks of lubricantleakage and/or contamination.

SUMMARY OF THE INVENTION

One embodiment of the invention relates to a work vehicle including aframe and an axle assembly coupled to the frame. The axle assemblyincludes an axle shaft and an axle housing. The axle shaft is disposedsubstantially within the axle housing, and a wheel is coupled to theaxle assembly. An axle lubricating fluid is disposed within the axlehousing. An axle cooling device is also disposed within the axlehousing, in contact with at least a portion of the lubricating fluid,and is configured as a coil including a plurality of elongate tubes.

Another embodiment of the invention relates to an axle assembly for awork vehicle. The axle assembly includes a first axle shaft and a firstaxle housing, and a second axle shaft and a second axle housing. Thefirst and second axle shafts are disposed substantially within the firstaxle housing and the second axle housing, respectively. The second axleshaft and the second axle housing are disposed coaxial with, and inopposing relationship to, the first axle shaft and the first axlehousing, respectively. This embodiment further includes a first coolingdevice disposed within the first axle housing, and a second coolingdevice disposed within the second axle housing. It further includes adifferential gearset housing positioned intermediate the first andsecond axle housings and defining a chamber configured to receive adifferential gearset. A differential gearset may also be included, andis disposed within the chamber and is rotatively coupled to the firstand second axle shafts. Further included are a lubricating fluiddisposed within the first and second axle housings. Still furtherincluded are a first axle cooling device including a first plurality ofelongate tubes and disposed within the first axle housing, and a secondaxle cooling device including a second plurality of elongate tubes anddisposed within the second axle housing.

Another embodiment of the invention relates to a method of cooling anaxle assembly of a work vehicle. The axle assembly includes an axleshaft, an axle housing configured to substantially surround the axleshaft, a cooling coil housed within the axle housing and having apassage therethrough and outer and inner surfaces, a lubricating fluiddisposed within the axle housing, and a cooling fluid disposed withinthe passage. The lubricating fluid is of a higher temperature than isthe outer surface of the coil, and the outer surface of the coil is of ahigher temperature than is the cooling fluid. The method includes a stepof removing heat from the lubricating fluid by placing the lubricatingfluid in contact with the outer surface of the coil. The method alsoincludes a step of removing the heat from the inner surface of the coilby circulating the cooling fluid through the passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rear sectional elevation of an axle assembly;

FIG. 2 is a schematic diagram of an embodiment of an axle coolingapparatus for cooling a single axle assembly;

FIG. 3 is a schematic diagram of an embodiment of an axle coolingapparatus for cooling two axle assemblies; and

FIG. 4 is a schematic diagram of an alternative embodiment of an axlecooling apparatus for cooling two axle assemblies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a work vehicle 10 provided with a frame 12, an axleassembly 14, wheels 16, and an axle cooling apparatus 18. Frame 12 maybe of any of the conventional types including fabricated steel or castiron. Axle assembly 14 and axle cooling apparatus 18 are describedbelow, and wheel 16 may be of any of the conventional types; e.g.,rubber-tired, cleated, or tracked. Wheels 16 support axle assembly 14with respect to a pavement or ground surface 20, and axle assembly 14supports frame 12. Only one axle assembly 14 is shown, but work vehicle10 may include any number of axle assemblies 14.

Axle assembly 14 includes at least one axle shaft 22 generally containedwithin an axle housing 24 and supported by axle housing 24 for rotativemovement relative to axle housing 24. Axle shaft 22 is of conventionalconstruction, typically machined of a medium-carbon steel and hardenedat least in the regions of splines (not shown). Axle housing 24 is alsogenerally of conventional construction (e.g., cast gray or ductile ironor fabricated of steel), but is of generally large transverse sectionalsize to accommodate a brake 26 and a cooling device, or coil 28 (bothdescribed below), as well as a planetary gearset (not shown). Axlehousing 24 may be of any transverse sectional shape; e.g., round,square, etc.

Brake 26, shown schematically in FIG. 1 as a single disk braked by acaliper, is, in an exemplary embodiment, a wet multidisk brake ofwell-known and conventional design. The term “wet” refers to a bath oflubricating fluid 30 that at least partially immerses brake 26,lubricating fluid 30 thereby providing both lubrication and cooling ofbrake 26.

A cooling device, shown as a coil 28 and a portion of cooling system 18(described below), is also housed within axle housing 24. Coil 28 is atubular device having a passage 32 provided internally therethrough, isof generally conventional construction and is fabricated of a pluralityof metal tubes 34, generally similar to a tube bundle of ashell-and-tube heat exchanger. In an exemplary embodiment, coil 28 isformed of a single length of tubing in one or more parallel “passes” bya series of 180 degree bends, providing a plurality of parallel tubelengths, each length connected to an adjacent length at one end so thatthe passes are disposed in series flow arrangement and coil 28 has oneinlet 36 and one outlet 38. In an alternative embodiment (not shown), acoil is fabricated of a plurality of cut tube lengths joined to eachother by “U”-shaped return bend fittings, themselves fabricated, ifnecessary, of a street elbow secured and sealed to a conventional elbow.In a further alternative embodiment, coil 28 includes fins, dimples, oris flattened to increase the surface area thereof in contact withlubricating fluid 30, and thereby to increase the heat transfer fromlubricating fluid 30 to coil 28.

Coil 28 is disposed near an inner bottom surface of axle housing 24 toensure its immersion in lubricating oil in various pitch and roll anglesof work vehicle 10. In an exemplary embodiment, at least the lowerportion of axle housing 24 is of a square transverse sectional shape sothat coil 28 may be formed of a flat sectional shape. In an alternativeembodiment, the transverse sectional shape of an axle housing isgenerally circular and the sectional shape of a coil is that of asegment of a circle having a slightly smaller radius than that of aninner surface of the axle housing.

Passage 32 within coil 28 is filled with a cooling fluid 40 (describedbelow). If cooling fluid 40 is of a high pressure (e.g., greater than 80pounds per square inch), coil 28 is preferably fashioned of a formablesteel tube material and secured to fittings by welding or brazing. Ifcooling fluid 40 is of a lower pressure, coil 28 may advantageously befashioned of a copper alloy (e.g., a soft brass) or an aluminum alloyfor higher thermal conductivity and therefore a higher rate of heattransfer.

Cooling fluid 40 may be any fluid, liquid or gaseous, with sufficientheat capacity and flow rate to remove braking heat from coil 28. Since,however, most examples of work vehicle 10, such as a loader, areprovided with hydraulic systems which include a hydraulic fluidgenerally maintained much lower than 300 degrees in temperature andotherwise suitable for removing heat from coil 28, in an exemplaryembodiment work vehicle 10 uses hydraulic fluid obtained from anexisting work vehicle hydraulic system as cooling fluid 40.

In operation, lubricating oil 30 receives heat from brake 26. Oil 30flows around coil 28. Coil 28 has outer and inner surfaces. Oil 30 has ahigher temperature than the outer surface of coil 28, and the outersurface of coil 28 has a higher temperature than cooling fluid 40. Thiscauses heat transfer from lubricating oil 30 to cooling fluid 40. Heatis removed from cooling fluid 40 as described below with respect to oneof FIGS. 2-4. FIG. 2 is a schematic diagram of an axle cooling circuit42 for an axle cooling apparatus 18 having one coil 28 for cooling of anaxle assembly 14. Cooling apparatus 18 is a portion of a much larger andmore complex hydraulic power circuit (not shown) connected at a coolingapparatus outlet port 64 and a cooling apparatus inlet port 66 fordriving actuators (not shown; e.g., power steering and brakes, bucketand boom lift and tilt, etc.). Cooling apparatus 18 includes coil 28, apump 44 (in an exemplary embodiment, an existing hydraulic system pumpof work vehicle 10) drawing hydraulic fluid, used as cooling fluid 40,from an existing system reservoir 46; an existing heat exchanger 48,shown as an oil cooler; a control valve 50, shown as a back pressureregulating valve (BPRV), and appropriate fluid conduits 52 (e.g., pipe,tube, hose).

Pump 44, reservoir 46, heat exchanger 48, and conduits 52 may befabricated from parts known to those of skill in the art. Coil 28 hasbeen described above. Control valve 50 is typically aspring-and-diaphragm or spring-and-piston apparatus having a pilot line54 in communication with the fluid whose pressure is to be controlled,fluid conducted by pilot line 54 applying pressure to the diaphragm orpiston in opposition to the force exerted by the spring, which isdisposed on an opposite side of the diaphragm or piston. A flowmodulating device (e.g., a valve plug or poppet) is rigidly secured tothe center of the diaphragm or the poppet, so that it moves in unisonwith the center of the diaphragm or the poppet in correspondence withthe pressure of the fluid and the spring rate of the spring. In anexemplary embodiment, control valve 50 is part number 4097 manufacturedby Shoemaker Inc., 12120 Yellow River Road, Fort Wayne, Ind. 46818 USA.

In an exemplary embodiment, heat exchanger 48 and coil 28 are fluidlydisposed in parallel with control valve 50. In this way, a smallpressure drop (e.g., 50 pounds per square inch) may be imposed bycontrol valve 50 to direct cooling fluid 40 through heat exchanger 48and coil 28 without substantially decreasing the efficiency of the workvehicle hydraulic system.

FIG. 3 is a schematic diagram of a cooling circuit 42 a for use with acooling apparatus of a work vehicle, the work vehicle further comprisinga second axle assembly, generally similar to first axle assembly 14described above. The second axle assembly is disposed coaxial with andin opposing relationship to the first axle assembly. In the embodimentshown in FIG. 1, the first axle assembly is the portion of axle 22 tothe left of differential gearset 58, and the second axle assembly is theportion of axle 22 to the right of differential gearset 58.

Cooling circuit 42 a includes a second coil 28 a, generally similar tofirst coil 28 described above. Second coil 28 a is fluidly disposed inparallel flow relationship to first coil 28. Inlet port 36 of first coil28 is in fluid communication with inlet port 36 a of second coil 28 a,and outlet port 38 of first coil 28 is in fluid communication withoutlet port 38 a of second coil 28 a. This provides a large flow area,and hence a high flow rate of cooling fluid through first coil 28 andsecond coil 28 a, allowing a high heat transfer rate with a relativelysmall and inexpensive first coil 28 and second coil 28 a.

FIG. 4 is a schematic diagram of a cooling circuit 42 b for use with acooling apparatus of a work vehicle, the work vehicle further comprisinga second axle assembly generally similar to first axle assembly 14described above. The cooling apparatus is similar to the coolingapparatus described above with reference to FIG. 3. In this embodiment,second coil 28 a is fluidly disposed in series flow relationship tofirst coil 28 by use of a connector, shown as a crossover conduit 56.Outlet port 38 of first coil 28 delivers cooling fluid 40 to inlet port36 a of second coil 28. This configuration provides a greater length oftime for any given particle of cooling fluid 40 to absorb heat fromcoils 28 and 28 a at a relatively low flow rate, providing a relativelylarge efficiency of cooling in terms of the quantity of thermal unitstransferred per unit of cooling fluid volume.

In any embodiment of axle assembly 14, first axle shaft 22 and a secondaxle shaft may be connected to opposite sides of a differential gearset58 (shown in FIG. 1). Generally, a differential housing 60, configuredto include a chamber 62 to accommodate differential gearset 58, is thenprovided to support and shield differential gearset 58 and to contain alubricant for differential gearset 58. Typically, this lubricant will besimilar to lubricating fluid 30, and one common bath of lubricatingfluid 30 may be used for lubrication of differential gearset 58 as wellas for lubrication and cooling of other parts of axle assembly 14.Crossover conduit 56 may then be given the bowed shape shown in FIG. 1in order to not interfere with differential gearset 58.

It will be understood that the foregoing description is of exemplaryembodiments of the invention, and that the invention is not limited tothe specific forms shown. Other modifications may be made in the designand arrangement of other elements without departing from the scope andspirit of the invention as expressed in the appended claims.

1. A work vehicle comprising: a frame; an axle assembly coupled to theframe and including a first axle shaft and a first axle housing, whereinthe first axle shaft is disposed substantially within the first axlehousing; a first wheel coupled to the axle assembly; an axle lubricatingfluid disposed within the first axle housing; a first axle coolingdevice disposed substantially within the first axle housing, in contactwith at least a portion of the lubricating fluid, including a firstcoil; a cooling fluid contained within the first coil, wherein the firstcoil is configured to conduct cooling fluid therethrough and to maintainthe cooling fluid separate from the lubricating fluid; a cooling fluidcircuit fluidly coupled to the first coil, wherein the cooling circuitincludes a cooling fluid pump and a cooling fluid reservoir, and whereinthe first coil receives cooling fluid from the pump and delivers coolingfluid to the reservoir; a heat exchanger to remove heat from the coolingfluid; a control valve disposed to direct at least a portion of thecooling fluid to the first coil at a predetermined pressure differenceacross the first coil; and a second wheel, wherein the axle assembly isfurther coupled to the second wheel and further includes a second axleshaft, a second axle housing, and a second coil, and further wherein thesecond axle shaft and the second coil are disposed substantially withinthe second axle housing, wherein an inlet of the second coil is in fluidcommunication with an inlet of the first coil and an outlet of thesecond coil is in fluid communication with an outlet of the first coil,and parallel flow paths are thereby provided through the first andsecond coils.
 2. An axle assembly for a work vehicle, the axle assemblycomprising: a first axle shaft and a first axle housing, wherein thefirst axle shaft is disposed substantially within the first axlehousing; a second axle shaft and a second axle housing, wherein thesecond axle shaft is disposed substantially within the second axlehousing, and wherein the second axle shaft and the second axle housingare disposed coaxial with, and in opposing relationship to, the firstaxle shaft and the first axle housing, respectively; a differentialgearset housing positioned intermediate the first and second axlehousings and defining a chamber configured therein to receive adifferential gearset, which is rotatively coupled to the first andsecond axle shafts; a lubricating fluid disposed within the first andsecond axle housings; a cooling device including a first axle coolingdevice disposed within the first axle housing, and a second axle coolingdevice disposed within the second axle housing; and a cooling fluidhoused within the first and second axle cooling devices, wherein thefirst and second axle cooling devices are configured to conduct coolingfluid therethrough and to maintain the cooling fluid separate from thelubricating fluid, wherein the first and second axle cooling devicesinclude first and second coils, respectively, each coil configured toprovide at least two passes of the cooling fluid through the lubricatingfluid within each of the first and second axle housings, and wherein aninlet of the second coil is in fluid communication with an inlet of thefirst coil and an outlet of the second coil is in fluid communicationwith an outlet of the first coil, and parallel flow paths are therebyprovided through the first and second coils.
 3. The axle assembly ofclaim 2, wherein the cooling device includes a cooling fluid pump and acooling fluid reservoir and the first and second coils receive coolingfluid flowing from the pump and deliver it to the reservoir.
 4. The axleassembly of claim 3, wherein the cooling device further includes a heatexchanger in fluid communication with the first and second coils.
 5. Theaxle assembly of claim 3, wherein the cooling device further includes acontrol valve for directing at least a portion of the cooling fluid flowto the first and second coils at a predetermined pressure differenceacross the first and second coils.
 6. The axle assembly of claim 5,wherein the control valve is configured as a back pressure regulatingvalve.
 7. A work vehicle comprising: a frame; an axle assembly coupledto the frame and including a first axle shaft and a first axle housing,wherein the first axle shaft is disposed substantially within the firstaxle housing; a first wheel coupled to the axle assembly; an axlelubricating fluid disposed within the first axle housing; a first axlecooling device disposed substantially within the first axle housing, incontact with at least a portion of the lubricating fluid, including afirst coil; a cooling fluid contained within the first coil, wherein thefirst coil is configured to conduct cooling fluid therethrough and tomaintain the cooling fluid separate from the lubricating fluid; acooling fluid circuit fluidly coupled to the first coil, wherein thecooling circuit includes a cooling fluid pump and a cooling fluidreservoir, and wherein the first coil receives cooling fluid from thepump and delivers cooling fluid to the reservoir; and a second wheel,wherein the axle assembly is further coupled to the second wheel andfurther includes a second axle shaft, a second axle housing, and asecond coil, and further wherein the second axle shaft and the secondcoil are disposed substantially within the second axle housing, whereinan inlet of the second coil is in fluid communication with an inlet ofthe first coil and an outlet of the second coil is in fluidcommunication with an outlet of the first coil, and parallel flow pathsare thereby provided through the first and second coils.
 8. An axleassembly for a work vehicle, the axle assembly comprising: a first axleshaft and a first axle housing, wherein the first axle shaft is disposedsubstantially within the first axle housing; a second axle shaft and asecond axle housing, wherein the second axle shaft is disposedsubstantially within the second axle housing, and wherein the secondaxle shaft and the second axle housing are disposed coaxial with, and inopposing relationship to, the first axle shaft and the first axlehousing, respectively; a differential gearset housing positionedintermediate the first and second axle housings and defining a chamberconfigured therein to receive a differential gearset, which isrotatively coupled to the first and second axle shafts; a lubricatingfluid disposed within the first and second axle housings; a coolingdevice including a first axle cooling device disposed within the firstaxle housing, and a second axle cooling device disposed within thesecond axle housing; and a cooling fluid housed within the first andsecond axle cooling devices, wherein the first and second axle coolingdevices are configured to conduct cooling fluid therethrough and tomaintain the cooling fluid separate from the lubricating fluid, whereinthe first and second axle cooling devices include first and secondcoils, respectively, and wherein an inlet of the second coil is in fluidcommunication with an inlet of the first coil and an outlet of thesecond coil is in fluid communication with an outlet of the first coil,and parallel flow paths are thereby provided through the first andsecond coils.
 9. The axle assembly of claim 8, wherein the coolingdevice includes a cooling fluid pump and a cooling fluid reservoir andthe first and second coils receive cooling fluid flowing from the pumpand deliver it to the reservoir.
 10. The axle assembly of claim 8,wherein the cooling device further includes a heat exchanger in fluidcommunication with the first and second coils.
 11. The axle assembly ofclaim 8, wherein the cooling device further includes a control valve fordirecting at least a portion of the cooling fluid flaw to the first andsecond coils at a predetermined pressure difference across the first andsecond coils.
 12. The axle assembly of claim 11, wherein the controlvalve is configured as a back pressure regulating valve.